Non-aqueous electrolytic solutions and electrochemical cells comprising the same

Abstract

A non-aqueous electrolytic solution for use in a lithium secondary battery has reduced or eliminated flammability and increased capacity retention. The electrolytic solution includes a lithium salt, a carbonate, a substituted phosphazene, a fluorinated solvent such as fluorinated carbonate, fluorinated ether, and fluorinated ester, and an organic phosphate or organic phosphonate such as fluorinated alkyl phosphate, fluorinated aromatic phosphate, fluorinated alkyl phosphonate, or fluorinated aromatic phosphonate.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is the U.S. National Phase of PCT / US2012 / 032960 filed Apr. 11, 2012, which claims priority of U.S. Provisional Patent Application 61 / 473,958 filed Apr. 11, 2011.BACKGROUND OF THE INVENTION[0002]1. Field of Invention[0003]The present invention relates to a non-aqueous electrolytic solution and an electrochemical energy storage device comprising the same. More particularly, this invention pertains to non-aqueous electrolytic solutions that comprise (a) one or more solvents; (b) one or more ionic salts; and (c) one or more additives. Non-aqueous electrolytic solutions capable of preventing fire or reducing flammability in energy storage electrochemical cells (e.g., lithium metal batteries, lithium ion batteries, lithium ion capacitors and supercapacitors) include a non-fluorinated carbonate, a lithium salt, a phosphazene compound, and a fluorinated solvent. Such electrolytic solutions enhance the battery performance, reduce ...

AI Technical Summary

Benefits of technology

[0009]The present invention arises due to the discovery by the inventors herein that together with solvents typically used in lithium or lithium ion batteries, the use of phosphazene compounds together with at least one of a fluorinated carbonate, a fluorinated ether, a fluorinated ester, a fluorinated alkane, a fluorinated phosphate and a fluorinated phosphonate, in the electrolytic solution of a lithium or lithium ion battery produces synergistic effects in terms of imparting non-flammability to the electrolytic solution, as well as reducing the concentration of both materials required for non-flammability, while maintaining or improving the performance of the cell. In particular, the present invention provides a secondary battery comprising an anode, a cathode, and an electrolytic solution.

[0010]The electrolytic solution includes a lithium salt and at least one carbonate with the addition of a fluorinated phosphazene coupled with at least one fluorinated aliphatic / aromatic compound and / or one fluorinated phosphate / phosphonate. The shorthand of the style “aliphatic / aromatic” or “phosphate / phosphonate” means that either or both can be present, that is an aliphatic compound and / or an aromatic compound can be present in one alternative, while a phosphate and / or phosphonate can be present in the other. The fluorinated aliphatic / aromatic compounds are selected from the group consisting of: fluorinated carbonates, fluorinated ethers, fluorinated esters, and fluorinated alkanes. The fluorinated phosphate / phosphonate compounds are selected from the group consisting of: fluorinated alkyl phosphates, fluorinated aromatic phosphates, fluorinated alkyl phosphonates, fluorinated aromatic phosphonates, and combinations thereof. The electrolytic solution may further contain other performance enhancing additives. The electrolytic solution of the invention is non-flammable, has low cost, and the electrochemical device containing the non-aqueous electrolytic solution has improved safety and cycle life.

[0011]Plainly stated, by the use of (1) a fluorinated phosphazene additive, together with an additive (2) which could be (2a) at least one fluorinated aliphatic / aromatic compound and / or (2b) at least one fluorinated alkyl / aromatic phosphate / phosphonate additive, allows the use of less total additives than would be possible when using either (1) or (2) alone, to achieve the same or similar reduction or elimination in flammability.

[0012]The present invention provides a non-aqueous electrolytic solution having no or low flammability, a long cycle life, and high capacity retention for lithium metal and lithium ion batteries using the same. In particular, the present invention provides a non-aqueous electrolytic solution having a cyclic and / or linear carbonate that is not fluorinated, a fluorinated phosphazene coupled with at least one fluorinated aliphatic or fluorinated aromatic compound (such as a fluorinated ether) and / or one fluorinated phosphate or fluorinated phosphonate compound, such as a fluorinated alkyl phosphate. The non-aqueous electrolytic solution includes a lithium salt dissolved therein.

[0016]Yet another embodiment of the invention is a secondary battery comprising: (a) an anode, (b) a cathode, and (c) an electrolytic solution comprising (i) a lithium salt, (ii) a first, non fluorinated carbonate, (iii) a phosphazene, (iv) a fluorinated compound selected from the group consisting of organic phosphate or organic phosphonate compounds selected from the group consisting of fluorinated alkyl phosphate, fluorinated aromatic phosphate, fluorinated alkyl phosphonate, and fluorinated aromatic phosphonate, and fluorinated ester, fluorinated alkane, and / or fluorinated carbonate, fluorinated ether. Such electrolytic solutions help to prevent or reduce flammability in a lithium secondary battery. Beneficial side effects may include the formation of a solid-electrolyte interface (SEI) on the negative electrode surface of the batteries, improved stability of the electrolytic solution, and increased interaction between the electrolytic solution and electrodes. Batteries utilizing electrolytic solutions with such compositions have long life, high capacity retention, and less risk of flammability.

Problems solved by technology

The conventional electrolytic solutions currently used in lithium or lithium ion batteries are highly flammable, and there is justifiable concern that in an accident situation a potential exists for leakage from the batteries, which would thus burn in the presence of flame or spark.

The high concentration required may cause a decrease in conductivity and can sometimes lead to deterioration in cell performance.

Another concern with such compounds is the cost: they are about 10 times more expensive than other materials used in the electrolytic solution.

This high concentration of materials may cause problems such as poor salt solubility, phase separation of the electrolytic solution itself, and the potential for loss of cell performance.

Because of the high costs and possibility of poor cell performance associated with high concentrations of conventional flame retardants, it is imperative to find alternative formulations and materials that may improve upon either or both of these problems.

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